Method to enhance polishing performance of abrasive charged structured polymer substrates

ABSTRACT

The intersection of discrete polishing islands staggered in a curvilinear shape with a workpiece maintains a substantially uniform film thickness throughout the polishing operation and also leading to a stable polishing operation due to the substantially invariant pressurization.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefits of the filing date of U.S. Provisional Patent Application Ser. No. 61/315,210 filed Mar. 18, 2010, which is entitled “Method to Enhance Polishing Performance of Abrasive Charged Structured Polymer Substrates” and U.S. Provisional Patent Application Ser. No. 61/315,237 filed Mar. 18, 2010, which is entitled “Method to Enhance Polishing Performance of Abrasive Charged Polymer Substrates” both of which are hereby incorporated herein in their entirety by reference.

FIELD OF THE INVENTION

The present invention is directed to a method and apparatus for an abrasive article with a plurality of polishing islands arranged to generate a constant contact area during polishing.

BACKGROUND

Polishing with polyamide or other polymer based substrate materials requires maintaining a constant hydrodynamic film for stability during the polishing operation and reducing the required hydrodynamic film is attainable by manufacturing a very large number of grooves into the polymeric film. Grooving of the polymeric film causes a reduction in the bearing area to enable interference between the diamond particles and the bar. The intersection of discrete polishing islands staggered in a curvilinear with a workpiece maintains a substantially uniform film thickness throughout the polishing operation and also leads to a stable polishing operation due to the substantially invariant pressurization.

The current method of polishing a magnetic slider bar onto a polyamide film populated with diamond abrasives attached to a lapping machine yields high localized deformation of the polymer substrate due to the large load required to overcome the hydrodynamic film formed by the lubricant during the lapping process. The dilemma of using a flexible substrate with the current state of the art lapping tools requires large loads to overcome the separation created by the hydrodynamic film formed due to the high shear viscosity of the lubricant and the bar geometry. To overcome the hydrodynamic film thickness and increase the interference between the bar and the polishing agent (substrate charged with diamonds) a large load is applied to the bar. The large load creates large deformation on the soft polymer causing edge rounding of the bar during the lapping process. FIGS. 1 and 2 show the stress concentration 103 at the corners of the bar lapping on a flexible polyamide substrate 104 subjected to large load 101 and in motion 102 with respect to the bar 106. The large deformation of the substrate causes the corners to be subjected to high stress concentration. Bar edges wear faster than the remaining areas; this initial accelerated wear levels off once the corners are rounded 105. Note that the edges of the bar house the critical transducers; such rounding causes a substantial head media spacing increase which is highly undesirable and has caused rejection of polyamide diamond charged substrate to gain use in finish slider bar polishing. Another factor contributing to the large deformation experienced by the polyamide arises from the applied preload to overcome the hydrodynamic film. FIG. 3 a shows a simulated hydrodynamic film 150 generated by a moving bar over water based lubricant. To achieve a hydrodynamic spacing of 100 nm a preload of over 100 Kg is required as depicted by the intersection of the horizontal line 151 with the oblique line 152.

Hydrodynamic film lubrication is desired to enhance the mechanical stability of the bar during the polishing however, if the hydrodynamic film thickness reaches a height greater than the diamond protrusion height polishing action is substantially reduced. So a balance between the hydrodynamic film thickness and the hydrodynamic pressure must be achieved to enhance polishing and also maintain a stable polishing operation. Mechanical stability maintains a chatter free operation and a predictable spacing between the bar and the polishing article. So maintenance of the mechanical stability is a must for a successful operation.

The following U.S. Pat. Nos. 6,277,160, 6,155,910, 6,322,652, and 7,300,479 show methods for fabricating structured abrasive on a flat carrier sheet of polyamide. The structured abrasive is formed of adhesive and diamond slurry cured on the carrier sheet. The structured abrasives are arranged in various configurations ranging from squares, trapezoidal, and rectangles. The arrangements proposed in prior art defined by the abovementioned patents do not conserve a constant hydrodynamic film under the bar during the polishing process. The uniform configurations shown in these patents and various sales brochures do not preserve a constant hydrodynamic lift during the polishing process.

FIG. 3 b gives an example of a trapezoidal shape organized uniformly. Creating large number of independent polishing islands help reduce the hydrodynamic film thickness, however, we will see the current arrangement of these polishing structures does not contribute at maintaining a uniform hydrodynamic film thickness. For illustrative purposes we introduce lines A and B representing a moving slider bar. The intersection of the lines A and B with the structured abrasives forms the area supporting the slider bar. The two intersections formed by A and B do not form a constant area leading to variable hydrodynamic film as the slider bar progresses leading to large modulation and chattering.

FIG. 3 c gives an example of a rectangular shape organized uniformly. For illustrative purposes, lines A and B represent a moving slider bar. The intersection of the lines A and B with the structured abrasives forms the area supporting the slider bar. Note that there is a likelihood that the slider bar does not get any support corresponding to the gaps between the structured abrasive islands causing a pressure drop and leading to large modulations and chatter. Note that area supporting the slider bar is not constant leading to variable hydrodynamic film leading to an undesirable condition.

FIG. 3 d gives an example of a rectangular shape organized uniformly on a circular substrate. For illustrative purposes, radial lines A and B represent a rotating slider bar with respect to the center of the abrasive consumable. The intersection of lines A and B form an area supporting the slider bar depending on the circumferential location of the slider bar. Note that there is a likelihood that the slider bar does not get any support at the discontinuity areas causing a pressure drop and leading to the chatter and aggressive interference. Note that area supporting the slider bar is not constant leading to variable hydrodynamic film.

FIGS. 3 b, 3 c and 3 d fail to produce a constant hydrodynamic film for polishing slider bars.

The traditional approach, as depicted in FIG. 4, of forming a series of concentric uniformly spaced grooves 203 designed to reduce the hydrodynamic film formed between the lapping bar 206 and the substrate 204 is explored for illustrative purposes. It is shown that it is necessary to substantially increase the number of grooves formed into the substrate to create a very large but finite number of grooves. The required preload 201 to cause a substantial reduction in polyamide bulk deformation must be reduced between one to two orders of magnitude from its current value. A very large number of grooves are fabricated into the substrate to help reduce the hydrodynamic lift force. Note that the groove depth must be sufficient to inhibit the formation of any hydrodynamic film over the grooved areas. It is highly desirable to keep the groove width to a minimum but assure that the depth is sufficiently large to inhibit the formation of a hydrodynamic film over the grooved during the polishing process.

SUMMARY OF THE INVENTION

FIG. 5 shows the hydrodynamic film pressure 252 formed over each land contained between grooves fabricated in the polyamide. A series of independent pressures are formed at each land. Summation of these individual pressures over the length of the bar balances the applied preload. Since the sides of each land is exposed to ambient pressure, a load bearing reduction is attained by breaking the overall length of the bar into small independent bearing areas compared to a continuous bar with the same overall length. Numerical simulations are useful in understanding the limits of the practice of fabricating spaced grooved patterns in the polyamide substrate.

FIG. 6 shows that attaining a preload reduction of twenty times from the original preload would require groove spacing of 30 nm. Manufacturing processes to achieve such feature size are highly complex and costly. It is very critical to create a very large number of grooves to reduce the fluid hydrodynamic film and reduce the required preload to provide enough spacing between the substrate and the polished bar. Grooving helps in two ways. First it establishes a multitude of individual pressure profiles over the bar contributing at its stability and the sum of the load carried by each individual fluid bearing is lower than the load carried by an equivalent fluid bearing with a length equal to the bar length. The side leakage of each fluid bearing contributes at reducing the load carrying capacity of each individual bearing. The lower preload required avoids deforming the polymeric substrate to a point of rounding the polishing article. The drawback of the solution of generating continuous and concentric grooves spaced with 30-100 nm is very difficult and challenging from a manufacturing viewpoint.

FIG. 7 shows a configuration with an engineering texture 302 applied to the polyamide 301 and grooves 303. The texture 302 causes high stresses at the interface. Thin film diamond like carbon 304 is applied to the polyamide to impart a hard surface. Subsequently a thin film lubricant is applied to enhance the lubrication of the interface. FIG. 8 shows a configuration 350 with abrasives 351 and a thin film lubricant 352 applied to the interface. Note that a thin film of diamond like coating 353 is applied to enhance the adhesion of the lubricant to the surface of the charged polyamide film can be very desirable in dry lubrication applications.

Another way to reduce the required applied load to cause desirable hydrodynamic spacing between the lapping bar and the diamond charged polyamide is discussed below. The solution includes reducing the film thickness generated by the shearing of the lubricant during the polishing process. Discrete sets of patterned islands are fabricated in the diamond charged substrate travel underneath the lapping bar causing a uniform hydrodynamic film regardless of the bar location on the substrate. A series of discrete islands are staggered and arranged to expose a substantially constant area under the slider bar. A novel island pattern organized to form a uniform film independent of bar location is presented. The uniform hydrodynamic film is maintained by maintaining a substantially uniform average pressure and a substantially uniform pressure center location as the bar moves with respect to the substrate. Discrete islands of the substrate cause substantial pressure side leakage to reduce the hydrodynamic pressure countering the applied preload.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a typical magnetic slider bar subjected to a large load for lapping purposes.

FIG. 2 shows the rounding of the corners of the slider bar due to the high stress concentration due to excessive penetration into the substrate due to large applied load and low modulus of elasticity of the polyamide.

FIG. 3 a: shows the relationship between the applied load and the film thickness between a bar and a polishing substrate lubricated with a water based lubricant.

FIG. 3 b prior art showing structured abrasive configurations in the form of lozenges.

FIG. 3 c prior art showing structured abrasive configurations in the form of rectangles.

FIG. 3 d prior art showing structured abrasive configurations in the form of rectangles stamped onto a circle.

FIG. 4 shows cross sectional view of a substrate having a series of concentric uniformly spaced grooves for reducing the hydrodynamic film formed between a lapping bar and the substrate.

FIG. 5 shows the pressure profile between each groove and bar.

FIG. 6 provides analysis of the hydrodynamic film formation in the presence of water as a lubricant.

FIG. 7 shows a textured polishing substrate with a series of grooves to reduce the hydrodynamic lift force emanating from the bar flying.

FIG. 8 showing the polishing substrate with a series of grooves to reduce the hydrodynamic lift force emanating from the bar flying.

FIG. 9 shows the staggered curvilinear diamond charged islands.

FIG. 10 shows a slider bar loaded onto the polishing article.

FIG. 11 offers a rectangular shaped substrate with a periodicity of 3 polishing islands spaced uniformly.

FIG. 12 offers a rectangular shaped substrate with a periodicity of 3 polishing islands spaced uniformly.

FIG. 13 offers a rectangular shaped substrate with independently arranged polishing islands

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein is the use discrete patterns arranged such that the slider bar is exposed to a substantially constant area of the polyamide. A polishing article 400 with staggered series of grooves 401, 402, and 403 repeating with a desired frequency is shown in FIG. 9. For example a series of uniformly spaced curvilinear patterns housing a series of islands are arranged on a circular substrate. For illustrative purposes we will assume that the bar width is equal to the polishing island width along the circumference of the substrate. As slider bar engages island A it disengages island C from the previous curvilinear segment of islands. As the spinning substrate engages island B under the bar, the slider bar disengages from island A leading to a constant area underneath the slider bar regardless of its location on the substrate. The benefit of this approach leads to a substantial reduction of the hydrodynamic film under a series of islands while maintaining a substantially uniform hydrodynamic film thickness.

Polishing islands offer a substantial reduction in pressure buildup due to the side leakage generated at the leading, trailing and side edges of the island. The curvilinear configuration shown in FIG. 9 preserves a constant area exposed under the slider bar leading to a substantially constant film thickness. The staggering of the curvilinear arcs contributes to a substantially uniform polish across the slider bar. We assume that the size of the discrete islands are equal to or smaller than the width of the slider bar. The slider bar is preferably exposed to the same polishing island (A for example) contained in the repeating patterns defined by the curvilinear arcs. Engaging pattern A, then progressively entering pattern B, and so forth and so on. This approach contributes to a significant reduction of area exposed under the slider while contributing to uniform polishing. FIG. 9 illustrates the example further by having all islands A engaging the slider bar first. The pressurization on the slider bar is uniformly spaced by the pattern A used in this example. Then pattern B is engaging so a partial pressure starts forming on the slider B while disengaging pattern A. As the pattern B is fully engaged pattern A is disengaged nullifying the pressurization gain from engaging pattern B. Geometrical design insures that as the pattern A is disengaged the slider bar maintains a constant hydrodynamic spacing by insuring a substantially constant area. FIG. 10 shows an apparatus for polishing a slider 450 whereas the slider bar 451 being polished by the diamond charged polyamide substrate 400.

FIG. 11 explores the example of a rectangular substrate charged with abrasives 500 subjected to a linear motion. The polishing islands 501 and 502 are organized to expose a constant area under the slider bar, such as slider bar 551 shown in FIG. 12. The illustrative example shows a pattern of 3 polishing islands A, B, and C spaced uniformly and repeating along both axes defining the plane of the substrate.

FIG. 12 shows an example with a periodicity of four polishing islands for illustrative purposes whereas a slider bar 551 sliding over a series of islands 552. The key to the design is the constant area under the slider to offer a uniform hydrodynamic film thickness. A rectangular bar 551 supported by a series of polishing island 552 is shown. As the bar moves from position 1 through position 3 the supporting area underneath the bar remain constant. For this illustrative example a slider bar with a width equals to twice the size of the island polishing pads is selected as an example. As the bar 551 moves from position 1 to position 2 the number of polishing islands supporting the bar remains constant. This approach guarantees that the center of pressure remains as constant as possible even though the pressure generated by each polishing island varies throughout the polishing process. The summation of the pressures generated by each individual polishing pad yields a substantially uniform pressure magnitude and a stationary pressure center location. The pressure magnitude and pressure center location are predictors of the hydrodynamic film thickness. The slider bar is subjected to an alternating pressure gradient with uniform pressure magnitude as the bar moves relative to the polyamide substrate. The center of pressure location is invariant throughout the polishing process. The bar attitude is substantially maintained by the proposed process.

FIG. 13 gives a detailed view of a polishing pad 600 used in conjunction with the present invention. A polishing pad assembly 610 is fabricated with an S-shaped link 620 to adjacent pads. The non-straight S-shaped links are arranged to connect the polishing pad with minimal out of plane resistance and contributes to decoupling the motion of each polishing pad from other adjacent pads. For example if a polishing pad 610 is deflected in the z plane perpendicular to the polishing pad assembly 610, the displacement experienced by the surrounding pads 611, 612, 613, and 614 will be small compared to the displacement of pad 610. The S-shape feature 620 has a low bending stiffness due to S shape allowing minimum cross talk between the pads when subjected to an in-plane or out of plane deflection. Non-straight shaped links such as Z, L, etc. can be arranged to further reduce the bending moment. In contrast, a straight connector generates tension on the adjacent polishing pads during a vertical or in-plane motion. Displacement due to in plane stretching of a straight connector requires very large forces to be produced thus limiting the amount of vertical displacement or in-plane displacement achieved by traditional configurations as shown in continuous polishing pad (500). So instead of fabricating a continuous sheet of carrier material a discontinuous sheet with S shape connector attaching adjacent independent polishing pad is desirable for providing low coupling forces between individual polishing pads.

Polyamide or other polymer based substrate materials require maintaining a constant hydrodynamic film for stability during the polishing operation and reducing the required hydrodynamic film is attainable by manufacturing a very large number of grooves into the polymeric film. The intersection of discrete polishing islands staggered in a curvilinear shape with a workpiece maintains a substantially uniform film thickness throughout the polishing operation and also leading to a stable polishing operation due to the substantially invariant pressurization.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these inventions belong. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present inventions, the preferred methods and materials are now described. All patents and publications mentioned herein, including those cited in the Background of the application, are hereby incorporated by reference to disclose and described the methods and/or materials in connection with which the publications are cited.

The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present inventions are not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.

Other embodiments of the invention are possible. Although the description above contains much specificity, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the presently preferred embodiments of this invention. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of at least some of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above.

Thus the scope of this invention should be determined by the appended claims and their legal equivalents. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem ought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims.

REFERENCES

-   Roche, S., Bec, S. and Loubet, J. L.: Analysis of the elastic     modulus of a thin polymer film. Mat. Res. Soc. Symp. Proc. 778,     117-122 (2003) -   Bec, S., Tonck, A., Georges, J. M., Coy, R. C., Bell, J. C. and     Ropper, G. W.: Relationship between mechanical properties and     structures of zinc dithiophosphate anti-wear films. Proc. R. Soc.     Lond. A 455, 4181-4203 (1999) -   Demmou, K., Bec, S., Loubet, J. L. and Martin, J. M.: Temperature     effects on mechanical properties of zinc dithiophosphate tribofilms.     Tribology International 39(12), 1558-1563 (2006) -   Bec, S., Tonck, A. and Loubet, J. L.: A simple guide to determine     elastic properties of films on substrate from nanoindentation     experiments. Philosophical Magazine A 86(33-35), 5347-5358 (2006) 

What is claimed is:
 1. An abrasive article for polishing a surface of a workpiece, the abrasive article comprising: a plurality of polishing islands arranged to interact with a workpiece to maintain a substantially constant contact area; and abrasive features associated with at least some of the plurality of polishing islands, the abrasive features applying cutting forces to the work piece during motion of the abrasive article relative to the workpiece.
 2. The abrasive article of claim 1 wherein the plurality of polishing islands form a curvilinear repeating and staggered arrangement for rotary polishing operations.
 3. The abrasive article of claim 1 wherein the plurality of polishing islands form a repeating and staggered island pattern for linear operations.
 4. The abrasive article of claim 1 wherein the plurality of polishing islands are arranged in a curvilinear form along the center of rotation of a circular polishing pad.
 5. The abrasive article of claim 1 wherein the plurality of polishing islands are pads arranged in a curvilinear form for a rotating pad.
 6. The abrasive article of claim 1 wherein the plurality of polishing islands are pads arranged at an oblique angle with respect to the workpiece.
 7. An abrasive article for polishing a workpiece, the abrasive article comprising: a plurality of polishing islands arranged to intersect with a workpiece to maintain a substantially constant contact area, wherein at least some of the polishing islands include a first surface engaged with the workpiece, and a second surface, attached to a polyamide substrate; and the plurality of polishing islands arranged in a cascade arrangement so as to cause a substantially invariant hydrodynamic film under the workpiece during motion of the abrasive article relative to the workpiece.
 8. The abrasive article of claim 7 wherein the first surface includes an abrasive feature comprising one or more of a nano-scale roughened surface coated with a hard coat, nano-scale diamonds attached to a trailing edge of the first surface, an abrasive particles attached to a film, or an abrasive composite.
 9. The abrasive article of claim 7 wherein the polishing pads include abrasive portions having a plurality of different lengths as measured along a direction of motion of the abrasive article relative to the substrate.
 10. An abrasive article for polishing a workpiece, the abrasive article comprising: a first polishing island: a second polishing island; and a non-straight link connecting the first polishing island and the second polishing island.
 11. The abrasive article of claim 10 further comprising a substrate of a polyamide material, the polyimide material coupled to the first polishing island and the second polishing island.
 12. The abrasive article of claim 10 further comprising a sponge like pad coupled to the first polishing island and the second polishing island, a preload placed onto the workpiece via a sponge like pad.
 13. The abrasive article of claim 10 wherein the first polishing pad and the second polishing pad are arranged in a curvilinear form along the center of rotation of a circular polishing pad.
 14. The abrasive article of claim 10 wherein the first polishing pad and the second polishing pad are arranged at an oblique angle with respect to the workpiece.
 15. An abrasive article for polishing a surface of a workpiece, the abrasive article comprising: a plurality of polishing islands arranged to intersect with a workpiece to maintain a substantially constant contact area; at least some of the plurality of polishing islands connected to other polishing islands with a non-straight link; and a polishing substrate containing abrasive features applying cutting forces to the work piece during motion of the abrasive article relative to the slider bar.
 16. The abrasive article of claim 15 including a curvilinear repeating and staggered polishing island arrangement for rotary polishing operations.
 17. The abrasive article of claim 15 including a repeating and staggered island pattern for linear operations.
 18. The abrasive article of claim 15 wherein the polishing pads are arranged in a curvilinear form along the center of rotation of a circular polishing pad.
 19. The abrasive article of claim 15 wherein the polishing pads are arranged in a curvilinear form for a rotating pad.
 20. The abrasive article of claim 15 wherein the polishing pads are arranged at an oblique angle with respect to the workpiece. 